Abstract: Orthogonal test was applied to investigate the ultrasonic bonding of platinum wire with a diameter of 20 μm.The microstructure of bonded area was observed and the height of bonded heel was measured with three-axis measuring microscope.The results indicate that the influence of bonding time, search height and ultrasonic power on the platinum wire tensile force was very notable,while the effect of bonding force was relatively small.The optimized bonding parameters with high efficiency could be obtained through orthogonal test.The optimum conditions are listed as follows:the bonding force was 0.013 N, the bonding power was 0.325 W,the bonding time was 30 ms, and the search height was 0.2 mm.The bonding quality could be evaluated by measuring the height of bonded heel.The tensile force of the bonded wire exceeded 0.03 N when the bonded heel was 4~10 μm.Meanwhile,it was likely to acquire high bonding quality when the welded area was in elliptical shape and the W was equal to approximately 2D.Tensile force was low when the welded area was in rectangular shape or micro cracks appeared.